Anti-ozidants



United States Patent ANTI-OZIDAN TS Edward L. Hill, Rock Island, Edwin R. Erickson, Moline, and Robert A. Berntsen, Rock Island, 111., assignors to Augustana Research Foundation, Rock Island, 111., a corporation of Illinois N0 Drawing. Application June 19, 1953, Serial No. 362,964

20 Claims. (Cl. 260-285) This invention relates to the preservation of rubber, and more particularly, to new rubber preservative compounds and compositions, which when incorporated in rubber tend to inhibit deterioration of rubber due to the action of heat, light and oxidation, and specifically due to the action of ozone.

As used herein the term rubber means solid resinous elastomer either natural or synthetic. As will be appreciated, the chemical structures of rubbers vary in certain respects, and rubber preservative compounds which might operate successfully with one given type of rubber may not function equally well with another given type of rubber. Heretofore, those skilled in the art have referred to rubber preservatives of the general class hereinbefore indicated as antioxidants, assuming that the oxidation deterioration of the rubber was brought about primarily by the presence of oxygen in the air. The instant invention, however, is based upon the discovery that ozone, which is ordinarily present in the air in only very small amounts, is a very critical factor in the rubber deterioration picture; and the instant invention is also based on the discovery of certain compounds which are effective antiozidants or compounds which effectively neutralize the deterioration effect of ozone.

As has been explained, a given antioxidant may be relatively effective with a given type of rubber, such as natural rubber, even though this antioxidant is only slightly or perhaps even not appreciably effective as an antioxidant for GR-S rubber. Also, it has been found that antioxidants which are particularly effective for a given type of rubber are substantially ineffective as antiozidants for this given type of rubber, and vice versa. It will thus be seen that the prior workers in the art having failed to appreciate the necessity for both the antioxidant and the antiozidant functions in rubber preservation have been unable to ofier a satisfactory solution to the rubber deterioration problem. In fact, the prior workers in the art had failed to appreciate the existence of the antiozidant function as such in the preservation of rubber and thus failed to comprehend completely the overall nature of rubber deterioration.

It is, therefore, an important object of the instant invention to provide an improved rubber preservative compound and/ or composition.

Another important object of the instant invention is to provide rubber having incorporated therein, as an antiozidant, (a) a compound having the formula:

incorporated therein, as an antiozidant, (a)a compound having the formula:

CH: CH: CH!

2,705,224 Patented M ar. 29 .1955

and the weight ratios of (a):(b):(c) being to 1 to"2:1 to 2:1 to 2 and (a) plus (b) plus ('0) equalling 5% of the elastomer.

Other objects, features and advantages of the instant invention will become apparent to those skilled in the art from the following detailed disclosure of preferred embodiments thereof. 1.

The instant invention is based upon the discovery that certain new compounds having repeating arylene diimino groups therein are uniquely superior for use as antiozidants in rubber and for use in combination with wax and/ or antioxidants in rubber compositions. These compounds have the following general formula:

wherein x is an integer from 1 to 30, each A is an arylene radical having from 1 to 2 benzene nuclei, each R is a C3-C6 alkyl radical and each X is a C2C10 alkylene radical. Each alkyl radical R may thus be a propyL'butyI, amyl or hexyl radical (as the n-, iso, sec. or tert. form); but preferably both Rs' are the same and are sec. alkyl radicals. Most preferably, been found to yield particularly superior results in GR-S rubber.

'The arylene radical A is, of course, a divalent aromatic radical which has 1 to 2 benzene nuclei, viz., phenylene, .biphenylene and naphthylene. If 2 benzene nuclei are present, preferably, the benzene nuclei are non-condensed as in the biphenylene radical. The imino (or sec. amine NH) substituents on the radical A are attached to different benzene nuclei, if more than one benzene nucleus is used in the radical A, and most preferably in a para arrangement as follows:

wherein R and R" are each alkyl radicals such as methyl, ethyl, propyl, buty etc. As will be explained hereinafter, the preferred reactant for forming this structure is diacetyl which results in the formation of the 1,2 dimethyl ethylene structure, as follows:

CH3 CH3 CH3 CH;

CH3 CH3 H- H- The three most effective antiozidants of the invention are:

N,N bis(p sec. butylaminophenyl) 2,3-butanediamine- CH: CHi

each R is see. butyl which has or the para-phenylene a 4 N,N' bis(p sec. butylarninobiphenyl) 2,3-butanedi- As previously mentioned, the foregoing reaction leads amineto monomer-polymer mixtures; but the monomer may'be CH3 CH3 and the polymer CH: CH;

In thefirsttwo compounds ",x is one; and in the polymer prepared in more pure form by the following reaction :c" is-rnore than one. sequence:

In the preparation of the antiozidants of the invention, (4) (K on: the characteristic reactions Involved may be represented p5 I as follows.

CL one (B m i 'NH: O: CH -N= CH NH HCH CH3 As will be seen Reaction 2 involves initial reduction of NO:; to NH2 and ls otherwise, similar to Reaction l y y s 1.; each of such reactions involving .a compound contain 99 A typical reaction for the preparation of the polymer agdlgrs g: figsttgfrhee taelzlove rfnelntioned preferred corn- SeebuQ-NH-ONH-dH-dH-NH-ONH-seebut.

0 ita )"H2 ai'J-C HaCHa As will be appreciated, if x is one, then the theoretical 50 amine is preparedby charging a Parr hydrogenator with yield will be only the N,N'-bis(p-sec. butylaminophenyl)- 75 g. of p-am'inoacetanilide, 200 ml. of methyl ethyl 'ke- 2,3-but-anediamine and no polymer would be obtained. It tone, '20 g. of the catalyst above described, and hydrohas been found, ,howa er, that a mixture of-monomer and gen at 1200-1575 lbs. per square inch and using a 'tempolymers is obtained even when it is one or less; but the perature of 130-160" 'C. for /2 hours. The catalyst is monomer may be-sepatatedout. Polymers when x is as v removed "by filtration and excess .ketone is removed high Q X' l fih Pmductlon of 1511011 distillationand the residue is poured into water, and re- P 31 5 5 gf g tg ii gy s they l crystallized from water-alcohol to yield silver plates meltgggi F g gg g 33535; 0 preven 6 ing .at 86-87 C. Acid hydrolysis to yield N-sec. butyl- Actually, the reaction is carried out in a hydrogen aty i i fonow'eid by fiammlizaiion mosphere at 500 to 2000 lbs. per square inch pressure and extract? andmsmlanon Ewe yellow hquld Pmdllct at temperatures of l30-l C. in the presence of a rethat 'bollsvat TMJS-QTQ 913 m of Hg findtllms Ted ducing catalyst, during the last of the process steps above upon exposure to air and light. This product (N-sec. described. 1

For example, substantially equimolecular portions of diace'tyl and p-phenylenediamine are condensed in boiling ethanol to form a mixtureof poly Schiflf bases, which Isleparates from the ethanol as an olive-green solid -W 'ic'h o does not melt at 325 C'.;?the average x in this mixture 21/2 hours ,7 temperatlne to obtain the is about 10. The product (26.6 g.) plus ml. of 7D E N* ff 1 methyl ethyl 'ketone and 7 g. of catalyst (CuO, Cr2O3 and ianedlamme, h lmnfied m The usual manner t charged in the L'Parr hydrogenator with 9.63 g. (0.112 mol) of diacetyl, 10 g. of catalyst, 125 ml. of benzene butyl p-phenylenediamine, 0.225 mol or 37 g.) is "then and hydrogen at i1000-1475 lbs. per square inch, using BaO) is charged into a Parr hydrogenator which in turn yield an amber viscous liquid boiling at 193-195 :C. atv is charged with hydrogen at 1000 lbs. per square inch 3 mm. of Hg. The biphenylene analogue is prepared by C and ream-0n (according the above Equdtifin carrying out the :same process except that'Neacet-ylbenzi- 3)'takes"place at'150-16'5" 'C. The reaction product was 1 removed, filtered to separate out the catalyst and subdmexs usedmplacg'ofN acetylpphenyxenfidlmnme' jected to reduced .pressure distillation to separate out In place of the dlacetyl other dbkew compounds unreacted and'Y or reduced :ketone. Ihe product is a thermo lastic resinousmaterial.

'I he phenylene monomer (i. e. the first of the above 8 z-i3'hexanedmne: 9 to 0 preferred compounds) is made by carrying out the same anemone- Such compounds that may be used include 2,3-pentanedimay be used, and preferably vicinal diketones are used.

reaction steps except that 2 mols of p-phenylenediamine In Place of mthyl fithyl ketone: the kew P are used for each mol of diacetyl. The benzidine anamay a t ne, diethyl ketOIlfl, y P PY f logues are prepared accordingly also by using henzidinein methyl propyl ketone, methyl hutyl ketone,

place of p-phenylenediamine. 85 The advantageous aspects of the'prcsent invention are mofe clearly demonstrated from the following formula- Stocks made from Formulation I are vulcanized to a comparable state of cure and subjected to a standard (air) oxidation test in a Geer oven and also subjected to exposure under stress of 20% elongation to atmosphere (100 F.) containing 25 p. p. h. in. (parts per hundred million) of ozone to determine the antiozidant characteristics. The oven temperature is 70 C.; and the original tensile of the stock is 2400; the tensile after 7 days in the Geer oven is 2400; and the tensile after 7 days exposure to the ozone Other stocks are subjected to outdoor weathering conditions, under stress of 20% elongation of the mbb noticeable cracks in one day under identical storage conditions).

Several rather unique aspects of the instant invention have been observed during the testing of stocks such as the above stocks as'well asstocks containing other antiozidants of the instant invention. For'example, it has been found that a unique synergistic effect is obtained by the combination of the instant antiozidant and wax. If the antiozidant is not used and only'the wax is incor-' porated in a formulation such as the above Formulation I, the antiozidant effect obtained is negligible, thereby indicating that neither the wax nor the antioxidant (alone or in combination) is capable of obtaining effective antiozidant properties in the stock. On the other hand, if the wax and not the antiozidant is omitted'from a formulation such as the above, it is found that the antiozidant properties are much less effective than those above indicated. This latter observation demonstrates clearly that the wax plays a very important part in the antiozidant picture, although the wax per se is-not effective as an antiozidant. The instant antiozidants are, of course, effective as such in the absence of wax, but an important aspect of the instant invention resides in the fact that the presence of the wax makes the instant antiozidants many fold more effective.

Waxes are a well known group of ingredients which, in general, are solids that are far too soft for structural purposes but are considered to be hard and non-greasy to the touch. Waxesmay be dispersed readily in the rubber composition during compounding; and W es have the additional advantage that they may be used to form a preliminary intimate mixture of the instant antiozidant and Wax, which mixture may be used to effect more rapid and complete dispersion of the two ingredients in the rubber during compounding. Also, it appears that the wax tends to preserve the antiozidant characteristics of the instant antiozidants, if the two materials are stored the weight ratio of antiozidant-to wax should be from 1:10 to 10:1, and more preferably from 1:2 to 2:1. Another peculiar aspect of theinstant'antiozidant-wax combination is that the amount of wax used in order to obtain maximum effectiveness may be as little as approximately the weight of the antiozidant (and one-half the weight is preferred), whereas the use other ingredients is usually assumed to involve amounts of wax that are many times the weight of the ingredient to be dispersed. Paraflin waxes are preferred, and microcrystalline waxes most preferred for use in the invention.

Still another important aspect of the instant invention of wax for dispersing various involves the use of the antioxidant in combination with the instant antiozidants. If the antioxidants are excluded from the above identified formulation, it will be found that the antioxidant characteristics of the stock are reduced, thereby clearly indicating the substantial ineffectiveness of the instant antiozidant (in the relatively small proportion used) as an antioxidant. It has been found that the instant antiozidants are substantially ineffective as antioxidants in practically all kinds of rubber; whereas any particular antioxidant which is effective in a given type of rubber, as an antioxidant, is substantially ineffective in such rubber as an antiozidant. Antiozidants for rubber were not heretofore recognized as a class of compounds; whereas antioxidants (of a great number of different types of compounds, many of which include amines) have been known for one or more different types of rubber. In general, the antiozidants of the instant invention are used in the same or somewhat smaller proportions by weight than the known antioxidants are used in a similar rubber composition. In fact, the instant antiozidants are preferably employed in weight proportions of about 1 to 2 parts per parts of rubber (although 1-5 parts may be used); whereas antioxidants are usually employed. in quantities of at least about 2 parts per 100 parts of rubber, in order to obtain effective antioxidant action. In the instant invention, the antiozidants per se are not appreciably effective antioxidants, nor are they used in quantities sufficient to obtain any appreciable antioxidant etfect, in the preferred formulations embodying the instant invention. 7

Subject to the above mentioned disclosure concerning the proportions used, the weight ratio of antiozidant to antioxidant may range from as much as 1:10 to 10:1, but the preferred range is about 1:2 to 2:1. As shown in the above Formulation I, the most preferred proportion is 1:1.

As has been'pointed out, antioxidants are known for use in rubber; and the instant invention contemplates the use of any of the known antioxidants for a given type of rubber, in combination with the instant antiozidants preferably, the antioxidants employed are substituted amines, amines (which are secondary amines), which contain a totalof 2 to 3 benzene nuclei in the molecule. Particularly satisfactory diaryl amine antioxidants include:

N-phenyl-B-naphthalamine and di-tolylamine (or homologues thereof)- is specifically described herein) isequally effective.

inert hydrocarbon structure in the molecule. planation is based on the theory that the effectiveness of the instant antiozidants is dependent at least in part to the particular positioning of the. H- group with respect to the benzene nucleus (to permit quinoid formation) and with respect to the alkyl group. The NH groups are thus preferably para (or ortho); and preferably attached to non-condensed benzene nuclei. the naphthylene analogues are effective antiozidants, but substantially less effective than the phenylene and biphenylene analogues.

If a type of rubber other than GR% is employed in the foregoing formulations, a distinct antiozidant effect is obtained using the antiozidants of the instant invention,

Thus.

but the antiozidant efiect obtained is not always as clearly superior as that obtained using wGR-S rubber, which is the preferred rubber for use in the instant invention. This indicates that the instant an'ozidants are particularly superior as such when used in the polybutadiene (synthetic) rubbers, and particularly in the butadiencstyrene copolymeric elastomer known by the trade name- GR-S Rubber. The polybutadiene rubbers are a well known class of synthetic rubbers which comprise essentially polymerized butadiene and also contain a relatively small amount (i. e., about 10%) of a copolymer, such as the styrene or the acrylonitrile copolyrners. The polybutadiene rubbers have been found to be particularly useful in connection with the instant antiozidants. Also, the instant antiozidants are efiective as such with other elastomers or rubbers, including natural rubber. The effectiveness of the instant antiozidant will, of course, depend to a certain extent upon the amount used, although it will be appreciated-that excessive amounts of the in stant antiozidant cannot be used as a practical matter. The total amount of antiozidant plus wax plus antioxidant is about 2-10% of the elastomer, and preferably about 5% of the elastomer. (As used herein, the terms parts and percent mean partsand percent by weight, unless otherwise designated.) It will be appreciated that somewhat larger as well as somewhat smaller amounts of these ingredients may be used, but appreciably larger amounts would be impractical from a cost point of view and also might cause interference with the functioning of other materials in the rubber such as the fillers. On

' respect to the particular rubber being used, might well zinc oxide and/ or carbon'black,-which are used as fillers in the rubber. The active ingredients (antiozidant, antioxidant and/or wax) are thus intimately admixed in 2 to 4 times their weight of such filler material so as to obtain a mixture which may be readily compounded with the rubber.

It will be understood that modifications and variations may be effected without departing from the scope of the novel concepts of the present invention.

We claim as our invention:

1. Rubber having incorporated therein,. as an antiozidant, (a) a compound having the formula:

having ina compound 4. Butadiene-styrene copolymeric elastomer having incorporated therein, as an antiozidant, (a) a compound having the-formula:

result in insuificiently effective antiozidant-antioxidant characteristics. In connection with the proportion of the antiozidant plus the wax, it is found that about 1-5 of 5. Butadiene-styrene copolymeric elastomer having incorporated therein, as an antiozidant, (a) a compound having the formula:

CH2 CH3 the elastomer is the preferred range, and the most preferred proportion is about 3%. These latter proportions are also the effective proportions for the antiozidant alone (in the absence of wax), since it is necessary to use more antiozidant, if wax parable effect.

As has been previously indicated, it is advantageous to obtain a preliminary mixture or dispersion of the instant antiozidants in another ingredient to be used therewith, such as the Wax, prior to using the rubber compounding operation. The instant antiozidant may also be preliminarily admixed with the antioxi' dants of the invention, in the proportions in which these is not used, in order to obtain a comthe instant antiozidant in (a):(b) ranging 6. Rubber having incorporated therein, as an antiozidant, (a) a compound having the formula:

wherein at is an integerfrom .1 to 30, each A is an arylene of from '1 to 2 unsubstituted benzene 1 radical consisting nuclei, each .R is a Ca-Cs alkyl radical and each X is .a (Dz-Cm alkylene radical and ('b) wax; the weight ratio of from 1:10 'to 10:1.

7. Butadiene-styrene copolyrneric elastomer having incorporated therein, as an antiozidant, (a) a compound having the formula:

era cm on:

ingredients will be used in the final rubber compounding; but it has been found to be particularly advantageous to adrnix all three ingredients, namely, the antioxidant, the antioxidant and the wax (in the proportions hereinbefore indicated), so that the resulting mixture may be made up and (b) wax; the weight ratio of (a) :(b) ranging from 1-:10to 10.21.

8. Butadiene-styrene copolymeric elastomer having in- V corporated therein, as an antiozidant, (a) a compound having the formula: 4

sacrum-NEGONH-dn-dH-+NHONE-sweat.

and (b) wax; the weight ratio of (a) :(b) ranging from 1:10 to 10: 1.

9. Butadiene-styrene copolymeric .elastomer having'incorporated therein, as an antiozidant, (a) a compound;

having the -formula:

-. CH3 -C'H3 l and (b) wax; the weight ratio of (a) :(b) ranging from wherein x is an integer from 1 to 30, each A is an arylene 1:10 to 10:1. radical consisting of from 1 to 2 unsubstituted benzene 10. A compound having the formula: nuclei, each R is a C3-C6 alkyl radical and each X is a r 5 Czh-Cio 1alkyletne radlcal (b()1 Ear; an% (e) anhantioxidan Y ot er tan te compoun a; te weigt ratio 0 R NH A NH L N A (a):(b):(c) being 1 to =1 to 101 to 10.

18. Butadiene rubber having incorporated therein, as wherein x 1s an integer from I to 30, each A is an arylene an antiozidant-antioxidant, (a) a compound having the radical consisting of from 1 to 2 unsubstituted benzene formula:

nuclei, each R is a C3-C6 alkyl radical and each X is a 10 C2-C1o alkylene radical.

1 1 A compound h i h f l Sec.a1kyl-N H-A-NH-L H- HNHA-NH-sec.alkyl 0 wherein each A is an arylene radical consisting of from 1 to 2 unsubstituted benzene nuclei and the sec.-alkyl Sec.alkyl-NH-ANH H- H-NHANH-sec.alkyl radicals each have three to four carbon atoms (b) wax and (c) a diarylamine antioxidant other than the comwherein each A is an arylene radical consisting of from pound (a); the weight ratio of (a) :(b) :(c) being 1 to 1 to 2 unsubstituted benzene nuclei and the sec.-alkyl 10:1 to 10:1 to 10.

radicals each have three to four carbon atoms. 19. Butadiene-styrene copolymeric elastomer having 12. N,N' bis(p-sec. butylaminophenyl)-2,3-butanediincorporated thereln, as an antiozidant, (a) a compound amine. having the formula:

CH: CH3 CH: CH:

(b) wax and (c) an antioxidant having the formula:

13. N,N' bis(p-sec. butylaminobiphenyl) -2,3-butane- NIL-Q diamine.

14. A compound having the formula:

and the weight ratios of (a):(b):(c) being 1 to 2:1 to OH; CH:

d o ition o inco oration alibi??? a iewiivtiieer, an iii timate mixture to 2 and pl an pl q alling 2-1o% of (a) a compound having the formula: of the elastomer.

20. Butadiene-styrene copolymeric elastomer having incorporated therein, as an antiozidant, (a) a compound wherein x is an integer from 1 to 30, each A is an arylene CH: CH;

radical consisting of from 1 to 2 unsubstituted benzene (b) wax and (c) an antioxidant having the formula: nuclei, each R is a C3-C6 alkyl radical and each X is a C2-C1!) alkylene radica1 and (b) wax; the weight ratio of (a):(b) ranging from 1:10 to 10:1 H 16. As an antiozidant-antioxidant composition for in- N corporation in rubber as a preservative therefor, an intimate mixture of (a) a compound having the formula:

and the weight ratios of (a):(b):(c) being 1 to 2:1 to wherein x is an integer from 1 to 30, each A is an arylene 231 2 and P P1118 q g radical consisting of from 1 to 2 unsubstituted benzene of the elastomernuclei, each R is a C3-C6 alkyl radical and each X is a o alkylene radical Wax and a antioxidant References Cited in the file of this patent other than the compound (a); the weight ratio of (ai :7(bl){: being 1 to 10:1 to 10:11:? 10. UNITED STATES PATENTS u er aving incorporate erein, as an antiozidant-antio 'dant, (a) acompound having the formula: 2l28945 Jones Sept 1938 FOREIGN PATENTS 479,919 Canada Jan. 1, 1,952 

1. RUBBER HAVING INCORPORATED THEREIN, AS AN ANTIOZIDANT, (A) A COMPOUND HAVING THE FORMULA: 